The standard power drill, and even a hand drill, has a chuck with a body formed with normally three angled guides holding jaws that can be moved axially forward and radially together to grip a tool on the chuck axis. The rear end of this chuck is fitted to a spindle of a drive unit so that a bit held by the jaws can be rotated. The disadvantage of such an assembly is that, whenever the bit must be changed, the user must laboriously retract the jaws and then advance them again after fitting the new bit to the chuck.
In recent times it has become standard to provide various bits, in particular screw bits, with a standardized 0.25 in (6.35 mm) hex shaft. Such bits are relatively easy to chuck and dechuck from the standard three-jaw chuck, and do not even have to be gripped that tightly as the faceted sides transmit torque very well. Nonetheless it is necessary to operate the chuck, typically by rotating a tightening ring, to chuck and unchuck even such hex-shank bits.
Some tools, particularly screw guns, are equipped with hex-seat sockets. Standard hex-shank bits can be snapped into and out of the socket. Often a retaining ring is pulled axially back to free a bit, but a bit can be chucked simply by being forced back into the socket on the chuck. This system is very convenient, but limits the power unit to use with such hex-shank bits.
It has been suggested to provide a hex-shank socket at the base of the tool recess of a standard three-jaw chuck. Such arrangements have some advantages, but are often clumsy to use and do not transmit torque efficiently between the bit and the drive unit.